The present invention is directed in general toward communication systems and, more particularly, toward a local area network including active stations wherein protection is provided for failed stations and/or open cables.
Local area networks are becoming more and more prevalent in today's world. With this widespread acceptance comes the need to improve the speed, efficiency and reliability of these systems. The present invention provides method and apparatus for improving the reliability of a local area network including active stations.
Local area networks generally include either passive or active stations. Local area networks having passive stations are those wherein a plurality of bus interface units (BIUs) are coupled to a common transmission line for transmitting information packets therebetween. These systems are desirable in that they allow stations, or BIUs, not having messages to transmit to remain idle, or inactive, while other stations occupy the transmission medium. This is commonly referred to as a broadcast medium.
Local area networks having active stations are those wherein a plurality of BIUs are coupled to a segmented transmission bus such that each BIU receives message packets from a predecessor station and transmits these message packets to a successor station. Commonly, the BIUs are arranged in a ring such that a BIU which originally transmits a message signal to a successor station will remove this message signal from the network when received from its predecessor station. However, these systems have proven unreliable in situations where a station fails, and, therefore, no message packets may be transmitted or received beyond that station. Further, communication may be lost in these systems when a cable is cut or otherwise open circuited. Therefore, it is desirable to provide a local area network having active stations wherein protection is provided against a failed station and/or an open cable.
One prior art method and apparatus for improving the reliability of local area networks including active stations is described as the star net. The star net provides means to short circuit each and every station coupled to the active ring by laying a plurality of cables to bypass open cables and short circuit failed stations. This star net topology is, however, a very costly solution to the reliability problem of an active station local area network.
It is, therefore, desirable to provide a local area network having active stations and providing reliable intercommunication therebetween. Particularly, it is desirable to provide a local area network having active stations wherein protection is provided against failed stations and/or an open cable. It is further desirable to provide such reliability without the need to resort to an expensive starnet topology.